Change in land use weakens Indian monsoon rainfall

Changes in land
use and land cover in India are weakening the monsoon rainfall over the Ganga
basin and north-east India, according to scientists at the Indian Institute of
Technology Bombay, Mumbai, and University of Nebraska, USA1. They came
to this conclusion by analysing satellite images taken over 18 years and
simulating the Indian monsoon through regional climate models with past and
present land use conditions.

The researchers have
shown how the conversion of forests into agricultural land has weakened the
Indian summer monsoon. The results provide a plausible explanation, if not
complete, for the decreasing trend in Indian summer monsoon rainfall since
1950.

In the 1980s, woody
savannas covered a significant part of central, peninsular and north-east
India. However, by 2005, much of this forest land disappeared, and croplands
dominated the landscape. In northeast India, forests were replaced by large
swaths of tea plantations.

Interestingly, the
reason for a dip in rainfall lies in the leaf area and roots of the plants.
Agricultural plants with shorter roots enable lesser water absorption by the
soil thereby reducing the amount of water evaporating from the earth’s surface.
Decrease in leaf area also results in low transpiration. This vicious cycle
results in a reduction recycled precipitation, and ultimately affects the
summer monsoon rainfall.

The study shows
that by incorporating changes in vegetation, it is possible to fine tune the
present climate models for a better future projection. The researchers now plan
to study other factors behind the decreasing Indian summer monsoon rainfall,
such as warming of the seas and aerosol forcing.

References

1. Paul, S. et al. Weakening of Indian summer monsoon rainfall due to changes in land use land cover. Sci. Rep. 6, 32177 (2016) doi: 10.1038/srep3217